1. Field of the Invention
An aspect of the present invention relates to an inverter for an electric vehicle, and more specifically, to an inverter for an electric vehicle, which enables a driver to maintain the driving sensation of the electric vehicle, similar to that in a vector control before a defect of a speed (position) sensor of the electric vehicle occurs, under a voltage/frequency (V/f) control, even when the vector control is impossible due to the defect.
2. Description of the Related Art
In general, an electric motor driven by an inverter operates in a speed control mode. The inverter receives a speed at which the electric motor is to be rotated, inputted from an outside (driver), and controls an output voltage of the inverter so that the electric motor is rotated based on instruction of the inputted speed.
On the other hand, an inverter for an electric vehicle does not directly receive the instruction of a speed inputted from an outside (driver) but controls an output voltage of the inverter in response to an input of an accelerator pedal installed in the electric vehicle. That is, if it is sensed that the driver has pushed the accelerator pedal, the electric vehicle continuously increases speed by increasing the rotational frequency of the electric motor in proportion to pushed degree of the accelerator pedal. If the driver pulls off his/her foot from the acceleration pedal, the inverter controls the electric vehicle to decrease speed by decreasing the rotational frequency of the electric motor through the generation of a zero output torque or reverse output torque of the electric motor.
The control method of the inverter for the electric vehicle is not a speed control method in which the inverter controls a speed of the electric motor by receiving the instruction of the speed, but may be a torque control method in which the inverter controls a torque of the electric motor based on the state of the accelerator pedal, which is a result (pushing the accelerator pedal when the speed is low and pulling off the his/her foot from the accelerator pedal or depressing a brake when the speed is high) obtained by driver's controlling the speed (rotational frequency of the electric motor) of the electric vehicle.
That is, the control of the electric motor is divided into a scalar control method that requires no input of a speed (position) sensor and a vector control method that requires a sensor. Generally, the vector control method capable of performing an instantaneous torque control is widely used in the control of the electric vehicle.
If the speed sensor tails under the driving of the electric vehicle, it is impossible to drive the electric vehicle using the vector control method. Therefore, it is required to develop an inverter for an electric vehicle, provided with a speed instruction generating unit for generating a speed instruction under a voltage/frequency control as a scalar control method so that a driver can maintain the existing driving sensation of the electric vehicle as it is.